Question

G protein-coupled receptors are important molecules involved in signal transduction.

Which statement about G protein-coupled receptors is true?
A. They are activated only by steroid hormones.
B. They bind both adenine and guanine nucleotides.
C. They generally contain seven membrane-spanning α helices.
D. They bind only guanine nucleotides.

Answer 1

C. They generally contain seven membrane-spanning α helices.

Step-by-step explanation:

The G protein-coupled receptors are components of signal transduction through G protein. Here, a plasma membrane receptor with seven transmembrane helical segments serves as a G-protein coupled receptor. These receptors are the integral membrane proteins and have seven hydrophobic regions of 20 to 28 amino acid residues.

These hydrophobic alpha-helices span the membrane back and forth seven times. Binding of a signaling molecule to the G-protein coupled receptor promoters a conformational change in the receptor’s intracellular domain. The activated receptor then triggers the replacement of bound GDP to the G protein by GTP and thereby activating it.